Business, science and entertainment applications depend upon computers to process and record data, often with large volumes of the data being stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved magnetic read/write heads, improved error correction techniques and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is now measured in hundreds of gigabytes on 512 or more data tracks.
FIG. 1 illustrates a traditional flat-lapped bi-directional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102, each equipped with a module 104. The bases are typically “U-beams” that are adhesively coupled together. Each module 104 includes a substrate 104A and a closure 104B with readers and writers 106 situated therebetween. In use, a tape 108 is moved over the modules 104 along a tape bearing surface 109 in the manner shown for reading and writing data on the tape 108 using the readers and writers 106. Conventionally, a partial vacuum is formed between the tape 108 and the tape bearing surface 109 for maintaining the tape 108 in close proximity with the readers and writers 106.
Two common parameters are associated with heads of such design. One parameter includes the tape wrap angles αi, αo defined between the tape 108 and a plane 111 in which the upper surface of the tape bearing surface 109 resides. It should be noted that the tape wrap angles αi, αo includes an inner wrap angle αi which is often similar in degree to an external, or outer, wrap angle αo. The tape bearing surfaces 109 of the modules 104 are set at a predetermined angle from each other such that the desired inner wrap angle αi is achieved at the facing edges. Moreover, a tape bearing surface length 112 is defined as the distance (in the direction of tape travel) between edges of the tape bearing surface 109. The wrap angles αi, αo and tape bearing surface length 112 are often adjusted to deal with various operational aspects of heads such as that of Prior Art FIG. 1, in a manner that will soon become apparent.
During use of the head of FIG. 1, various effects traditionally occur. FIG. 2 is an enlarged view of the area encircled in FIG. 1 FIG. 2 illustrates a first known effect associated with the use of the head 100 of FIG. 1. When the tape 108 moves across the head as shown, air is skived from below the tape 108 by a skiving edge 204 of the substrate 104A, and instead of the tape 108 lifting from the tape bearing surface 109 of the module (as intuitively it should), the reduced air pressure in the area between the tape 108 and the tape bearing surface 109 allows atmospheric pressure to urge the tape towards the tape bearing surface 109.
As data density increases, gap-to-gap distance between the modules (gaps being where the elements are located) becomes more important. For example, in read-while-write operation, the readers on the trailing module read the data that was just written by the leading module so that the system can verify that the data was written correctly. If the data is not written correctly, the system will recognize the error and rewrite the data. However, the tape does not move across the tape bearing surfaces perfectly parallel to the tape guides. Rather, the tape may shift transversely by unequal amounts on each side of the head as it crosses the tape bearing surfaces, resulting in dynamic skew, or misalignment of the trailing readers with the leading writers. The effects of skewing are exacerbated as track density increases because the margin of error, defined as writer width minus reader width, decreases. And the farther the readers are behind the writers, the more chance that track misregistration will occur. If it does occur, the system may, for example, incorrectly believe that a write error has occurred.
Further exacerbating the misregistration problem is that stresses may develop during the module-joining process and these may disrupt track to track alignment and tape bearing surface planar alignments.
One approach currently being investigated by the present inventor is use of a three module tape head. A conventional alignment system would use a complex system of u-beams, that additionally require complex angular alignments. Furthermore, the resultant mass of the head assembly places greater demands on the head positioning actuator, which is a major consideration for future formats. In addition, such an alignment approach suffers from the same stresses that tend to disrupt track to track alignment and tape hearing surface planar alignments.
There is accordingly a clearly-felt need in the art for a tape head assembly having multiple modules, yet overcomes some or all of the drawbacks mentioned above.